This invention relates generally to fluid-delivery systems and more particularly to one including a pump having its own internal, low-volume-capacity bypass valve. Proposed by the invention, in such a system, is a high-volume-capacity, auxiliary-overload-bypass valve for relieving a defined high pressure condition which can occur in the system when the pump is overworking and the system is not delivering fluid--a condition not "protectible" by the pump's internal bypass valve.
Conventional home-heating fuel delivery systems, wherein the invention offers particular utility, are designed for use on a fuel-delivery truck. One end of such a system is coupled to the truck's deliverable fuel supply, and the other end to a delivery nozzle for use by the operator.
Such a system includes fuel plumbing which feeds fuel into a fuel pump, connects an output of the pump to a meter, and couples an output of the meter to a flexible hose which is connected to a delivery nozzle. The pump's speed can be accelerated to an RPM sufficient to pump fuel through the entire system. Increasing the pump's speed produces a full-fuel-delivery-pressure condition in the system so that, once the operator opens the nozzle, fuel is deliverable at a suitable rate.
To operate the pump, the same is coupled to the truck's transmission by way of an auxiliary drive shaft. Then, by increasing the truck-engine RPM, the operator increases the pump's speed to a full-fuel-delivery rate, approximately 600 RPM which produces a full-fuel-delivery pressure of 50-100 psi throughout the system. Given this pressure and the standard two-inch diameter pipe used in conventional systems, such systems deliver fuel at 50-100 gpm.
To deal with certain system-pressure-overload conditions, a conventional system's pump includes an internal-overload-bypass valve designed to relieve system pressure when the pump is operating at full-fuel-delivery speed and the delivery nozzle is closed. These conventional valves allow the system operator to run the pump without having to deliver fuel.
Specifically, the internal-overload-bypass valve is capable of relieving system pressure when the pump is operating at full-fuel-delivery speed, i.e. 600 RPM, producing full-fuel-delivery pressure of 50-100 psi throughout the system. Because conventional overload bypass valves have been designed to deal with the above, so-called, "normal" system pressure, they have been dimensioned to divert fuel at a rate suitable for such a purpose, i.e. 40-50 gpm.
However, conventional systems are not capable of dealing with greater-than-full-fuel-delivery pressure exceeding 100 psi. A common cause of such an extreme condition is failure of the system operator to disengage the auxiliary drive shaft from the truck's transmission after completing fuel delivery and before leaving the delivery site.
With the auxiliary drive shaft engaged while the operator increases the truck-engine RPM to drive the truck, the pump will be overworked. Specifically, the pump's speed will increase to greater than 600 RPM because the operator increases the truck's engine speed to power the truck. This greater-than-full-fuel-delivery speed of the pump causes an extreme pressure build-up in the delivery system of up to several hundred psi. At such extreme pressures, any and all components in the system are likely to rupture because the system pressure exceeds that which the components are rated to withstand.
Not only is the delivery system damaged, but there is also the problem of fuel oil being wasted. Finally, the condition is expensive because several people-hours of cleanup are required.
A proposed solution to the problem has been to provide a system with an electric pump shut-off mechanism. This proposal is flawed in as much as the above-described, extreme pressure build-up and resultant system damage could still occur if the shutoff is defective. In such a case, the operator will not know if the defect exists until it is too late, i.e. until a component of the system ruptures.
Thus, conventional overload-bypass valves are unable to prevent such system failure because they can only handle "normal" system pressure caused by operating the pump at full-delivery speed. Further, conventional internal bypass valves are relatively low-volume valves which are unable to transfer the high volume of fuel at a rate necessary to relieve pressure.
It is therefore a primary object of the present invention to provide a high-volume-capacity auxiliary-overload-bypass valve connected across the pump in such a system for shunting the pump and relieving above-normal system pressure that occurs when the pump is overworking and the system is not delivering fuel.
Another important object of the invention is to provide an auxiliary-overload-bypass valve that can shunt a fuel pump so that fuel is diverted at a rate suitable to relieve greater-than-full-delivery pressure caused when the pump is overworking.
Still another object of the invention is to provide an integrated system as generally described that is easy to operate and simple to incorporate in prior-art systems.
To overcome the problems of the prior art, the system of the present invention includes a auxiliary-overload-bypass valve which can be positioned externally or internally of the pump to provide important backup for the pump's usual internal bypass valve. This auxiliary valve includes a valve body having an inlet connected to a portion of the delivery system downstream of the pump, and an outlet connected to a portion of the system upstream of the pump. Disposed within the valve body is a valve-opening mechanism for relieving system pressure by allowing fuel to pass through the body when the system reaches a greater-than-full-fuel-delivery pressure caused by overworking of the pump.
These and other objects and advantages offered by the present invention will be more clearly understood from a consideration of the accompanying drawings and description of the preferred embodiment.